In the field of dispensable liquid cleaning and disinfecting substances, a wide range of liquids are used. Many of these liquids evolved from the use of soap and detergent bars for handwashing. Bar soaps are economical, long lasting and an effective way to dispense small quantities of a sparingly soluble material, soap, for handwashing. Unfortunately, bar soaps, even when they contain an antimicrobial agent, are also excellent vehicles for transmission of microorganisms from one user to another.
One of the earliest widespread uses of liquid handwashing compounds was in hospital scrub environments. These handwashing compounds incorporated a variety of antibacterial agents for use in surgical scrub protocols and hospital infection control procedures. The surfactant component of the compound serves to disperse the antimicrobial agents on the practitioner's skin with the water used for washing and to facilitate the removal by the wash water of materials on the skin surface that could harbor microorganisms.
In the surgical scrub application, the liquid handwashing products serve primarily as a delivery system for delivery of antimicrobial agents onto the practitioner's skin so that microorganisms are removed or rendered non-viable. Many of these liquid antimicrobial agents are not particularly water soluble. Thus if a large droplet of a not particularly easily dispersible handwashing liquid is dispensed, considerable effort is required to distribute the agent over the practitioner's skin. To facilitate the practitioner's use of these antimicrobial handwashing compounds, dispensing devices that form a foam from the liquids were developed. When foamed, most of these handwashing compounds are significantly more easily dispersed in manual handwashing than the same compound in the liquid, unfoamed, state, because by being foamed, the surface area of the material is greatly increased. There are other benefits of foamed compounds: a) since the compound is readily dispersed, practitioners tend to use significantly less of the product while accomplishing the same desired effect of the surgical scrub procedure; and less water is needed to disperse the compound, the effective concentration of the antimicrobial compounds on the skin is likely higher than with the same liquid in a non-foamed state. A variety of different antimicrobial handwashing compounds are now available with many different types of antimicrobial agents. The physical attributes of these antimicrobial handwashing compounds vary from materials with viscosities not much higher than water, i.e. about five to about thirty-five centipoise (cps), to viscosities similar to motor oil or hand lotions, i.e. up to about one hundred cps, and up to about one thousand six hundred, similar to a cream.
U.S. Pat. No. 4,957,218 to Ford discloses a foam dispenser that utilizes manually created negative air pressure to fill a pump from a larger container with a foamable liquid and manually created positive air pressure to displace the liquid into a mixing chamber where a foam is formed from mixing the air and the liquid. The device disclosed in this patent is effective with low viscosity (ca. five to about thirty-five cps) liquids as a substrate, but with more viscous liquids (ca. about fifty to about one hundred cps), the foam produced is low density, i.e. high air content, and perceived as "dry" by users.
Another U.S. Pat. No. 5,411,177 to Blake discloses a foam dispensing apparatus that includes a liquid container and a foam generating device. The foam generating device has a plurality of passages through which pressurized gas flows simultaneously with foamable liquid into the foam generating chamber past a flow restricter. Again, the device disclosed in this patent produces acceptable foam with low viscosity liquids. Liquids having a viscosity greater than about twenty cps are not well dispensed by the device described in this patent.
If a foam dispensing device were available that was capable of forming acceptable foam with handwashing antimicrobial liquids over a range of viscosities, the efficiency of use of these handwashing compounds in hospital infection control protocols and other applications would be advanced. Such a device is disclosed hereinbelow.